f(x)=√2sin(2x-π/4)
x∈[π/8,3π/4]
∴2x∈[π/4,3π/2]
2x-π/4∈[0,5π/4]
∴sin(2x-π/4)∈[-√2/2,1]
∴√2sin(2x-π/4)∈[-1,√2]
最大值=√2
最小值=-1